1. Field of the Invention
The present invention relates generally to communication systems for computer networks. In particular, the present invention relates to a system and method for sending and responding to information requests in a wireless communications network. Still more particularly, the present invention relates to a non-persistent method of transmitting and receiving data.
2. Description of the Related Art
During the recent past, the use of computer communication networks has become widespread. Included in the development of computer communication networks is the advent of the wireless communication network. Referring now to FIG. 1, a block diagram of a prior art wireless communications system 20 is shown. The wireless communications system 20 comprises a plurality of node computer systems 22 that are positioned within a predetermined distance of each other for sending and receiving messages via radio signals. A particular node, A, can receive signals from any one of the plurality of nodes 22 within a predetermined bounding zone or range as delineated by the circular area 24. Each of the other nodes 22 is also able to receive signals within a range, where each respective node is at the center of the range. The nodes 22 are effectively linked together for communication with each other using a particular channel or frequency for transmitting and receiving signals.
One problem with such wireless networks is that they have only very limited bandwidth. Unlike traditional wire networks, there is no dedicated line coupling the nodes to each other. Because of Federal regulations pertaining to certain frequency bands, the network can only operate a small predetermined amount of time (typically 400 ms) on any one channel, and the signals must be within a narrow frequency band thereby limiting the number of channels available. Thus, the bandwidth for wireless networks to transfer information is severely limited. This significantly impacts the amount of information that can be carried over the network.
Another problem is network flooding. Many network systems provide a class of general broadcast messages or information requests that are sent over the network, and to which any node on the system can respond. Such information requests are sent over the network, and one or more nodes will prepare response messages to provide the information requested. The response messages are then sent over the network back to the requesting node. However, the process of sending a request message often has the effect of flooding the network with multiple redundant response messages responding to the initial request. Unfortunately, these response messages can degrade performance of the network until all the response messages have been delivered to the requesting node. In distributed network systems where multiple nodes may respond, no solution to this network flooding problem has been found. Moreover, the problem of network flooding is even more severe on wireless networks because of their limited bandwidth.
The prior art has attempted to reduce the effects of network flooding using a variety of techniques. One such technique has been to designate a single node as a master node, and to have the master node respond to all messages in the general broadcast class. However, the problem with this method is that the node designated to be master undergoes serious performance degradation because of the added responsibility of having to respond to all the general information requests. The added responsibility creates further problems because it interferes with the normal operation of the master node. Moreover, the nodes in wireless networks are often mobile computers designed for portability. The nodes will continuously move in and out of the range of the wireless network, therefore, it is very difficult to choose a master node and be sure that the master node will always be connected to the network as required for master nodes.
A second technique used to reduce the effects of network flooding has been to designate a group or subset of nodes as masters in an attempt to distribute the costs and burden of responding to the information requests. However, this technique creates other problems. The major shortcoming of the second technique is the difficulty in selecting the appropriate subset of nodes. The appropriate subset of nodes depends on the number of nodes coupled to the network. Since the number of nodes in a wireless network can fluctuate greatly, it is difficult to select the appropriate number of nodes to designate as masters. If the network is small (has very few nodes) and the set of master nodes is large, many duplicate responses will be generated and the reduction of network flooding is minimal. On the other hand, if the network is large (has many nodes) and the set of master nodes is small, any request for information must be generated and sent many times before a response is received. This second technique also requires additional overhead for monitoring the number of master nodes and maintaining the number of master nodes at an appropriate level since a node that is designated a master node may lose contact with the network as it moves outside the range of the network.
Therefore, there is a need for a system and method that effectively eliminate the flooding problems exacerbated by the limited bandwidth of wireless networks. Moreover, there is a need for a system and method that can reduce the effects of flooding even in truly distributed systems on wired networks.